Methods and apparatuses for voltage regulation using precharge rails

ABSTRACT

A voltage regulator circuit using precharge voltage rails is generally disclosed. For example, the voltage regulator circuit may include a first voltage regulator having a voltage output, an output capacitor coupled to the voltage output, and one or more precharge voltage circuits configured to selectively couple to the voltage output, each of the one or more precharge voltage circuits comprising a capacitor coupled between an output of a precharge voltage regulator and a reference potential.

TECHNICAL FIELD

Certain aspects of the present disclosure generally relate to electronic circuits and, more particularly, to a voltage regulator circuit.

BACKGROUND

A wireless communication network may include a number of base stations that can support communication for a number of mobile stations. A mobile station (MS) may communicate with a base station (BS) via a downlink and an uplink. The downlink (or forward link) refers to the communication link from the base station to the mobile station, and the uplink (or reverse link) refers to the communication link from the mobile station to the base station. A base station may transmit data and control information on the downlink to a mobile station and/or may receive data and control information on the uplink from the mobile station. The base station and/or mobile station may include one or more power amplifiers (PAs) to amplify signals for transmission.

To increase power efficiency of the mobile station, average power tracking (APT) may be used to adjust the supply voltage to a discrete voltage to the one or more PAs based on the output power level of the amplified signals to be transmitted during a transmission period. The supply voltage may be provided by a voltage regulator capable of adjusting the output voltage to the discrete voltage to be supplied to the one or more PAs. However, a transient delay exists between changing the output voltage between the discrete voltages. Depending on the amount of transient delay, there may not be enough time to sufficiently adjust the discrete voltage to a different value for the next transmission period. Accordingly, it would be beneficial to find solutions to reduce the transient delay when changing between discrete voltages.

SUMMARY

Certain aspects of the present disclosure generally relate to improving the output voltage response of an adjustable voltage regulator using precharge rails.

Certain aspects of the present disclosure provide for a voltage regulator circuit. The voltage regulator generally includes a first voltage regulator having a voltage output, an output capacitor coupled to the voltage output, and one or more precharge voltage circuits configured to selectively couple to the voltage output, each of the one or more precharge voltage circuits comprising a capacitor coupled between an output of a precharge voltage regulator and a reference potential.

Certain aspects of the present disclosure provide for a method for regulating voltage using one or more precharge voltage circuits. The method generally includes determining a target output voltage to be supplied by a voltage regulator and providing the target output voltage via the voltage regulator by at least coupling a precharge voltage circuit having a capacitor charged to a voltage level substantially equal to the target output voltage to a voltage output of the voltage regulator.

Certain aspects of the present disclosure provide for a voltage regulator circuit. The voltage regulation circuit generally includes a switching voltage regulator having a voltage output coupled to a supply line of one or more power amplifiers and a plurality of voltage rail prechargers each configured to selectively provide a voltage to the voltage output.

Certain aspect of the present disclosure provide for a voltage regulator circuit. The voltage regulator circuit generally includes means for providing a regulated voltage to a voltage output, means for precharging a plurality a voltage rails to a plurality of respective voltages, and means for selectively coupling a voltage rail of the plurality of voltage rails to the voltage output based on a voltage level of the regulated voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the present disclosure can be understood in detail, a more particular description, briefly summarized above, may be had by reference to aspects, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only certain typical aspects of this disclosure and are therefore not to be considered limiting of its scope, for the description may admit to other equally effective aspects.

FIG. 1 is a diagram of an example wireless communications network, in accordance with certain aspects of the present disclosure.

FIG. 2 is a block diagram of an example access point (AP) and example user terminals, in accordance with certain aspects of the present disclosure.

FIG. 3 is a block diagram of an example transceiver front end, in accordance with certain aspects of the present disclosure.

FIG. 4 is a block diagram of a voltage regulation circuit using precharge rails in accordance with certain aspects of the present disclosure.

FIG. 5 is a block diagram of an average power tracking (APT) voltage regulator circuit, in accordance with certain aspects of the present disclosure.

FIG. 6 is a block diagram of the APT voltage regulator circuit of FIG. 5 using power multiplexers, in accordance with certain aspects of the present disclosure.

FIG. 7 is a block diagram of an APT voltage regulator circuit using switching regulator output switches, in accordance with certain aspects of the present disclosure.

FIG. 8 is a block diagram of an APT voltage regulator circuit using two adjustable precharge voltage circuits, in accordance with certain aspects of the present disclosure.

FIG. 9 is a block diagram of an APT voltage regulator circuit using two switching regulators, in accordance with certain aspect of the present disclosure.

FIG. 10 is a block diagram of the APT voltage regulator circuit 1000 using two switching regulators and a capacitor switch network, in accordance with certain aspects of the present disclosure.

FIG. 11 is an example operation of a voltage regulation method using precharge voltage rails, in accordance with certain aspects of the present disclosure

DETAILED DESCRIPTION

Various aspects of the disclosure are described more fully hereinafter with reference to the accompanying drawings. This disclosure may, however, be embodied in many different forms and should not be construed as limited to any specific structure or function presented throughout this disclosure. Rather, these aspects are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Based on the teachings herein, one skilled in the art should appreciate that the scope of the disclosure is intended to cover any aspect of the disclosure disclosed herein, whether implemented independently of or combined with any other aspect of the disclosure. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. In addition, the scope of the disclosure is intended to cover such an apparatus or method which is practiced using other structure, functionality, or structure and functionality in addition to or other than the various aspects of the disclosure set forth herein. It should be understood that any aspect of the disclosure disclosed herein may be embodied by one or more elements of a claim.

The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects.

As used herein, the term “connected with” in the various tenses of the verb “connect” may mean that element A is directly connected to element B or that other elements may be connected between elements A and B (i.e., that element A is indirectly connected with element B). In the case of electrical components, the term “connected with” may also be used herein to mean that a wire, trace, or other electrically conductive material is used to electrically connect elements A and B (and any components electrically connected therebetween).

An Example Wireless System

FIG. 1 illustrates a wireless communications system 100 with access points 110 and user terminals 120, in which aspects of the present disclosure may be practiced. For simplicity, only one access point 110 is shown in FIG. 1. An access point (AP) is generally a fixed station that communicates with the user terminals and may also be referred to as a base station (BS), an evolved Node B (eNB), or some other terminology. A user terminal (UT) may be fixed or mobile and may also be referred to as a mobile station (MS), an access terminal, user equipment (UE), a station (STA), a client, a wireless device, or some other terminology. A user terminal may be a wireless device, such as a cellular phone, a personal digital assistant (PDA), a handheld device, a wireless modem, a laptop computer, a tablet, a personal computer, etc.

Access point 110 may communicate with one or more user terminals 120 at any given moment on the downlink and uplink. The downlink (i.e., forward link) is the communication link from the access point to the user terminals, and the uplink (i.e., reverse link) is the communication link from the user terminals to the access point. A user terminal may also communicate peer-to-peer with another user terminal. A system controller 130 couples to and provides coordination and control for the access points.

Wireless communications system 100 employs multiple transmit and multiple receive antennas for data transmission on the downlink and uplink. Access point 110 may be equipped with a number N_(ap) of antennas to achieve transmit diversity for downlink transmissions and/or receive diversity for uplink transmissions. A set N_(u) of selected user terminals 120 may receive downlink transmissions and transmit uplink transmissions. Each selected user terminal transmits user-specific data to and/or receives user-specific data from the access point. In general, each selected user terminal may be equipped with one or multiple antennas (i.e., N_(ut)≥1). The N_(u) selected user terminals can have the same or different number of antennas.

Wireless communications system 100 may be a time division duplex (TDD) system or a frequency division duplex (FDD) system. For a TDD system, the downlink and uplink share the same frequency band. For an FDD system, the downlink and uplink use different frequency bands. Wireless communications system 100 may also utilize a single carrier or multiple carriers for transmission. Each user terminal 120 may be equipped with a single antenna (e.g., to keep costs down) or multiple antennas (e.g., where the additional cost can be supported). In certain aspects of the present disclosure, the access point 110 and/or user terminal 120 may include at least one voltage regulator to adjust the supply voltage for one or more power amplifiers (PA), as described in more detail herein.

FIG. 2 shows a block diagram of access point 110 and two user terminals 120 m and 120 x in the wireless communications system 100. Access point 110 is equipped with N_(ap) antennas 224 a through 224 ap. User terminal 120 m is equipped with N_(ut,m) antennas 252 ma through 252 mu, and user terminal 120 x is equipped with N_(ut,x) antennas 252 xa through 252 xu. Access point 110 is a transmitting entity for the downlink and a receiving entity for the uplink. Each user terminal 120 is a transmitting entity for the uplink and a receiving entity for the downlink. As used herein, a “transmitting entity” is an independently operated apparatus or device capable of transmitting data via a frequency channel, and a “receiving entity” is an independently operated apparatus or device capable of receiving data via a frequency channel. In the following description, the subscript “dn” denotes the downlink, the subscript “up” denotes the uplink, N_(ap) user terminals are selected for simultaneous transmission on the uplink, N_(dn) user terminals are selected for simultaneous transmission on the downlink, N_(up) may or may not be equal to N_(dn), and N_(up) and N_(dn) may be static values or can change for each scheduling interval. Beam-steering or some other spatial processing technique may be used at the access point and user terminal.

On the uplink, at each user terminal 120 selected for uplink transmission, a TX data processor 288 receives traffic data from a data source 286 and control data from a controller 280. TX data processor 288 processes (e.g., encodes, interleaves, and modulates) the traffic data {d_(up)} for the user terminal based on the coding and modulation schemes associated with the rate selected for the user terminal and provides a data symbol stream {s_(up)} for one of the N_(ut,m) antennas. A transceiver front end (TX/RX) 254 (also known as a radio frequency front end (RFFE)) receives and processes (e.g., converts to analog, amplifies, filters, and frequency upconverts) a respective symbol stream to generate an uplink signal. The transceiver front end 254 may also route the uplink signal to one of the N_(ut,m) antennas for transmit diversity via an RF switch, for example. The controller 280 may control the routing within the transceiver front end 254. Memory 282 may store data and program codes for the user terminal 120 and may interface with the controller 280.

A number N_(up) of user terminals 120 may be scheduled for simultaneous transmission on the uplink. Each of these user terminals transmits its set of processed symbol streams on the uplink to the access point.

At access point 110, N_(ap) antennas 224 a through 224 ap receive the uplink signals from all N_(up) user terminals transmitting on the uplink. For receive diversity, a transceiver front end 222 may select signals received from one of the antennas 224 for processing. The signals received from multiple antennas 224 may be combined for enhanced receive diversity. The access point's transceiver front end 222 also performs processing complementary to that performed by the user terminal's transceiver front end 254 and provides a recovered uplink data symbol stream. The recovered uplink data symbol stream is an estimate of a data symbol stream {s_(up)} transmitted by a user terminal. An RX data processor 242 processes (e.g., demodulates, deinterleaves, and decodes) the recovered uplink data symbol stream in accordance with the rate used for that stream to obtain decoded data. The decoded data for each user terminal may be provided to a data sink 244 for storage and/or a controller 230 for further processing. The transceiver front end (TX/RX) 222 of access point 110 and/or transceiver front end 254 of user terminal 120 may include at least one PA as described in more detail herein.

On the downlink, at access point 110, a TX data processor 210 receives traffic data from a data source 208 for N_(dn) user terminals scheduled for downlink transmission, control data from a controller 230 and possibly other data from a scheduler 234. The various types of data may be sent on different transport channels. TX data processor 210 processes (e.g., encodes, interleaves, and modulates) the traffic data for each user terminal based on the rate selected for that user terminal. TX data processor 210 may provide a downlink data symbol streams for one of more of the N_(dn) user terminals to be transmitted from one of the N_(ap) antennas. The transceiver front end 222 receives and processes (e.g., converts to analog, amplifies, filters, and frequency upconverts) the symbol stream to generate a downlink signal. The transceiver front end 222 may also route the downlink signal to one or more of the N_(ap) antennas 224 for transmit diversity via an RF switch, for example. The controller 230 may control the routing within the transceiver front end 222. Memory 232 may store data and program codes for the access point 110 and may interface with the controller 230.

At each user terminal 120, N_(ut,m) antennas 252 receive the downlink signals from access point 110. For receive diversity at the user terminal 120, the transceiver front end 254 may select signals received from one of the antennas 252 for processing. The signals received from multiple antennas 252 may be combined for enhanced receive diversity. The user terminal's transceiver front end 254 also performs processing complementary to that performed by the access point's transceiver front end 222 and provides a recovered downlink data symbol stream. An RX data processor 270 processes (e.g., demodulates, deinterleaves, and decodes) the recovered downlink data symbol stream to obtain decoded data for the user terminal.

FIG. 3 is a block diagram of an example transceiver front end 300, such as transceiver front ends 222, 254 in FIG. 2, in which aspects of the present disclosure may be practiced. The transceiver front end 300 includes a transmit (TX) path 302 (also known as a transmit chain) for transmitting signals via one or more antennas and a receive (RX) path 304 (also known as a receive chain) for receiving signals via the antennas. When the TX path 302 and the RX path 304 share an antenna 303, the paths may be connected with the antenna via an interface 306, which may include any of various suitable RF devices, such as a duplexer, a switch, a diplexer, and the like.

Receiving in-phase (I) or quadrature (Q) baseband analog signals from a digital-to-analog converter (DAC) 308, the TX path 302 may include a baseband filter (BBF) 310, a mixer 312, a driver amplifier (DA) 314, and a power amplifier (PA) 316. The BBF 310, the mixer 312, and the DA 314 may be included in a radio frequency integrated circuit (RFIC), while the PA 316 may be external to the RFIC. The BBF 310 filters the baseband signals received from the DAC 308, and the mixer 312 mixes the filtered baseband signals with a transmit local oscillator (LO) signal to convert the baseband signal of interest to a different frequency (e.g., upconvert from baseband to RF). This frequency conversion process produces the sum and difference frequencies of the LO frequency and the frequency of the signal of interest. The sum and difference frequencies are referred to as the beat frequencies. The beat frequencies are typically in the RF range, such that the signals output by the mixer 312 are typically RF signals, which may be amplified by the DA 314 and/or by the PA 316 before transmission by the antenna 303.

The RX path 304 includes a low noise amplifier (LNA) 322, a mixer 324, and a baseband filter (BBF) 326. The LNA 322, the mixer 324, and the BBF 326 may be included in a radio frequency integrated circuit (RFIC), which may or may not be the same RFIC that includes the TX path components. RF signals received via the antenna 303 may be amplified by the LNA 322, and the mixer 324 mixes the amplified RF signals with a receive local oscillator (LO) signal to convert the RF signal of interest to a different baseband frequency (i.e., downconvert). The baseband signals output by the mixer 324 may be filtered by the BBF 326 before being converted by an analog-to-digital converter (ADC) 328 to digital I or Q signals for digital signal processing. In certain aspects of the present disclosure, the PA 316 may implement average power tracking (APT) using a voltage regulator with precharge rails to adjust the supply voltage of PA 316, as described in more detail herein.

While it is desirable for the output of an LO to remain stable in frequency, tuning the LO to different frequencies typically entails using a variable-frequency oscillator, which involves compromises between stability and tunability. Contemporary systems may employ frequency synthesizers with a voltage-controlled oscillator (VCO) to generate a stable, tunable LO with a particular tuning range. Thus, the transmit LO frequency may be produced by a TX frequency synthesizer 318, which may be buffered or amplified by amplifier 320 before being mixed with the baseband signals in the mixer 312. Similarly, the receive LO frequency may be produced by an RX frequency synthesizer 330, which may be buffered or amplified by amplifier 332 before being mixed with the RF signals in the mixer 324.

While FIGS. 1-3 provide a wireless communication system as an example application in which certain aspects of the present disclosure may be implemented to facilitate understanding, certain aspects provided herein can be applied to amplify signals in any of various other suitable systems.

Example Voltage Regulator Circuit

For voltage regulators having an adjustable voltage output, an amount of time is required to step between voltages within a voltage range of operation (e.g., 0.4V to 2V). The voltage regulator may have to step between a minimum value of the voltage range of operation to the maximum value of the operating range within a time period depending on the requirements of an application. As applications may continually require more stringent requirements as to the time for output voltage changes, it would be beneficial to reduce the time it takes for a voltage regulator to step between output voltages.

Referring now to FIG. 4, a block diagram of a voltage regulation circuit 400 using precharge rails in accordance with certain aspects of the present disclosure. The voltage regulation circuit comprises a voltage regulator 402 configured to adjust the voltage of an output voltage (Vout) provided at the output of the voltage regulator 402. The voltage regulator 402 may be configured according to various voltage regulator topologies. For example, the voltage regulator may comprise a linear regulator (e.g., a low dropout (LDO) regulator) or a switching regulator (e.g., buck, buck-boost, boost).

The voltage regulation circuit 400 further comprises n number of precharge voltage circuits 404 each having an output that is selectively coupled to the output of the voltage regulator 402. The precharge voltage circuit may be referred to as a precharger. Each of the precharge voltage circuits 404 are configured to store a voltage corresponding to one of the output voltage levels that the voltage regulator 402 is configured to provide as an output voltage Vout. In one implementation, the voltage is stored using an output voltage provided by the voltage regulator 402 to a precharge voltage circuit 404. In another implementation, each of the precharge voltage circuits 404 comprise a voltage regulator configured to provide the voltage to be stored.

During a change from a current target output voltage level to a next target voltage level, the precharge voltage circuit 404 having a stored voltage substantially corresponding to the next target voltage level (e.g., within a voltage tolerance or including a voltage offset) is coupled to the output of the voltage regulator 402. By coupling the precharge voltage circuit 404, the output voltage is pulled to the voltage stored in the precharge voltage circuit 404 which may allow for a quicker output voltage transitions as compared to a voltage regulator not implementing precharge voltage circuits. In one implementation, the voltage regulator 402 may have one or more feedback comparators (not shown) each set to an available target output voltage of the voltage regulator 402. When the voltage regulator 402 is changing to the next target output voltage, the feedback comparator set to the corresponding voltage may be coupled into a feedback loop (not shown) used to adjust the output voltage of the voltage regulator 402. By using the one or more feedback comparators, an amount of time is takes for the voltage regulator 402 to adjust the output voltage to the next target voltage level may be improved.

In one implementation, a plurality of the precharge voltage circuits 404 may be located together on a voltage hub (not shown) and connected to a plurality of voltage regulators 402 which may be located remotely from the voltage hub. Each of the precharge voltage circuits 404 may be configured to selectively couple to the output of one of the voltage regulators 402 via the voltage hub. In one implementation, the voltage hub further comprises a plurality of switches configured to couple a precharge voltage circuit 404 to an output of the voltage hub coupled to one of the plurality of voltage regulators 402. An exemplary benefit of the voltage hub is that each of the voltage regulators 402 may independently source current to a load (e.g., power amplifier supply line) by selectively coupling to a different precharge voltage circuit 404 of the voltage hub to a load.

Example Average Power Tracking Voltage Regulator Circuit

It may be desirable for power amplifiers (PAs) used for standards such as 5G millimeter wave (mmWave) to implement average power tracking (APT). APT adjusts the supplied voltage to a power amplifier according to the output power level of a signal to be transmitted to improve power efficiency while maintaining linearity of the power amplifier. In 5G mmWave, the output power level may be adjusted every 9.8 microseconds. In some implementations, to support APT in 5G mmWave, the voltage regulator may need to step from a first voltage level (e.g., 0.8V) to a second voltage level (e.g., 2V) within a required time period (e.g., 100 nanoseconds). This required time period may be based on an operational requirement of a desired settling time within a portion of a symbol to be transmitted (e.g., cyclic prefix). Certain aspects of the present disclosure provide a voltage regulation circuit that allows for output voltage changes within increasingly demanding time periods.

Referring to FIG. 5, is a block diagram of an average power tracking (APT) voltage regulator circuit 500, in accordance with certain aspects of the present disclosure. The APT voltage regulator circuit 500 comprises a switching regulator 502. In one implementation, the switching regulator 502 comprises a buck converter configured to step down an input voltage to a target output voltage at an output voltage node 503. The switching regulator 502 further comprises an output inductor 504 coupled to a first terminal of an output capacitor 506. A second terminal of the output capacitor 506 is coupled to a reference potential (e.g., ground). The output voltage node 503 is further coupled to a voltage supply line for a power amplifier array 508 comprising one or more power amplifiers 510 configured to amplify signals for transmission. In one implementation, the power amplifier array 508 comprises four power amplifiers 510 a-d.

The APT voltage regulator circuit 500 further comprises a plurality of precharge voltage circuits 404. In one implementation, each of the precharge voltage circuits 404 comprises a precharge voltage regulator 511, a capacitor 512 coupled between an output of the voltage regulator 511 and ground, and a switch 514. The precharge voltage regulator 511 may comprise a linear regulator (e.g., an LDO) or a switching regulator (e.g., a buck converter). Each of the precharge voltage circuits 404 are configured to store an amount of voltage (i.e., voltage level) by charging the capacitor 512. For example, each precharge voltage circuit 404 may store a different amount of voltage corresponding an available voltage output of the switching regulator 502. The amount of voltage stored by each precharge voltage circuit may comprise a fixed voltage amount or the precharge voltage circuit 404 may be configured to adjust the voltage amount to be stored between different amounts of voltages.

Switches 514 are configured to selectively couple/decouple a respective precharge voltage circuit 404 from the output voltage node 503. The precharge voltage circuit 404 coupled to the output has a stored voltage level that substantially corresponds to a set output voltage amount of the switching regulator 502. For example, when the switching regulator 502 has a set output voltage of 0.8V, the precharge voltage circuit 404 configured to store 0.8V is coupled to the output voltage node 503 while the remaining precharge voltage circuits 404 are decoupled from the output voltage node 503. When the switching regulator 502 steps to a next target output voltage (e.g., 2V), the precharge voltage circuit 404 that is currently coupled to the output voltage node 503 is decoupled while the precharge voltage circuit configured to store a voltage level that substantially corresponds to the next target output voltage (e.g., 2V) is coupled to the output voltage node 503. To avoid a potential shoot-through current through a precharge voltage circuit due to a voltage mismatch, a precharge voltage circuit 404 is decoupled from the output voltage node 503 prior to coupling the precharge voltage circuit 404 corresponding to the next target output voltage. By coupling the precharge voltage circuit 404 having an amount of voltage stored corresponding to a target output voltage to the output voltage node 503, the output voltage is more quickly brought up to the target output voltage than by using the switching regulator 502 alone.

It should be noted a speed at which a switching regulator may change between voltage levels may be dependent on the capacitance of the output of the switching regulator (i.e., bulk capacitance). A smaller bulk capacitance may result in a fasting switching time between voltage levels. However, the transient response of the switching regulator in response to load attacks may be negatively impacted as the charge current available to compensate for the load attack is reduced as capacitance is decreased. In one implementation, the capacitors 512 of the precharge voltage circuits 404 may be selected to comprise a capacitance size constituting a majority of the bulk capacitance of the APT voltage regulator circuit 500 when coupled to the output voltage node 503. Additionally, the output capacitor 506 may be selected to constitute a minority of the bulk capacitance. For example, the capacitance of each capacitor 512 of the precharge voltage circuits may be ten times larger (e.g., 10 microfarads) compared to the capacitance of the output capacitor 506 (e.g., 1 microfarad). Accordingly, the switching time between voltage levels of the switching regulator 502 may be reduced by implementing an output capacitor 506 with a smaller capacitance while still providing for a larger overall bulk capacitance via the capacitors 512 having larger capacitance to compensate for load attacks.

When switching between target output voltage levels, there may be a voltage error associated between switching from a current target output voltage level to the next target output voltage level. This voltage error may be due to charge sharing between the output capacitor 506 charged at the current target output voltage level when coupling the capacitor 512 having a voltage level corresponding the next target output voltage level to the output voltage node 503. An exemplary cause of the voltage error will now be discussed with respect to Equations 1-3. The charge of a capacitor is given by Equation (1). Q=CV  Eq. (1):

-   -   where: Q=charge stored in a capacitor     -   C=capacitance of the capacitor; and     -   V=voltage of the capacitor         As the output capacitor 506 and the capacitor of the coupled         precharge voltage circuit will be connected in parallel,         Equation (2) provides from the combination of the charges of the         output capacitor and capacitor 512.         Q _(Final) =Q ₁ +Q ₂  Eq. (2):     -   where: Q₁=charge of the output capacitor; and     -   Q₂=charge of the capacitor of the precharge voltage circuit         In view of Equation (2), the final output voltage will be given         by Equation (3).         V _(Final)=(C ₁ V ₁ +C ₂ V ₂)/(C ₁ +C ₂)  Eq. (3):     -   where: C₁=capacitance of the output capacitor     -   V₁=current target voltage     -   C₂=capacitor of precharge circuit; and     -   V₂=next target voltage stored on C₂         As can be seen by Equation (3), the voltage error between the         final voltage V_(Final) is a function of capacitor sizes of the         output capacitor 506 and the capacitor 512 of the precharge         voltage circuit 404 and their respective voltages. Accordingly,         knowing the capacitance values and the current and next target         voltages, a voltage offset can be determined to either be added         or subtracted by the precharge voltage regulator 511 to the         voltage amount stored on the capacitor 512 corresponding to the         next target voltage to improve the output voltage accuracy when         changing between output voltages. The amount of the voltage         offset can be stored in a predefined lookup table (LUT)         containing a voltage offset for possible output voltage         transitions. Alternatively, a LUT may be updated by comparing         the output voltage when a precharge voltage circuit is coupled         to the voltage output rail compared to the target output         voltage. The difference between the output voltage and the         target output voltage can be used to update the LUT. By updating         the LUT, the APT voltage regulator circuit 500 can account for         voltage errors caused by operational conditions due to capacitor         de-rating and/or capacitor aging. The LUT may be updated         continually or only when an error threshold is met and/or         exceeded.

To charge the capacitors 512 of the precharge voltage circuits 404, the APT voltage regulator circuit 500 may implement an initialization phase. In one implementation, the initialization phase comprises decoupling the precharge voltage circuits 404 from the output voltage node 503 and charging the capacitors 512 using a respective precharge voltage regulator 511 to a target amount of voltage. In another implementation, the capacitors 512 are charged using the output voltage of the switching regulator 502. The capacitors 512 may be charged by the switching regulator 502 outputting a target amount of voltage and coupling the precharge voltage circuit 404 configured to be charged to a voltage level corresponding to the target amount. The remaining precharge voltage circuits may be decoupled. Alternatively, the switching regulator 502 may charge the capacitors 512 by initially coupling the precharge voltage circuits 404 to the output voltage node 503 and cycling the output voltage from the lowest voltage level and gradually stepping up between the voltage amounts to be stored in the precharge voltage circuits 404. When the output voltage exceeds a voltage level to be stored in precharge voltage circuit 404, the respective precharge voltage circuit 404 is decoupled from the output voltage node 503. This process continues until the capacitors 512 of the precharge voltage circuits 404 are charged to their corresponding target voltage amounts. An exemplary benefit of using the switching regulator 502 to charge the capacitors 512 is that the precharge voltage regulators 511 of the precharge voltage circuits may be configured to retain the voltage stored on the capacitors which may be reduced, for example, by capacitor leakage. As the precharge voltage regulators 511 may only be compensating for the leakage, as compared to fully charging the capacitors, a smaller voltage regulator may be used which may reduce costs and provide area savings.

Referring now to FIG. 6, is a block diagram of the APT voltage regulator circuit of FIG. 5 using power multiplexers, in accordance with certain aspects of the present disclosure. The APT regulator circuit 600 includes a plurality of multiplexers 602 capable of handling the output voltages of the switching regulator 502 (i.e., power multiplexers), each of the power multiplexers 602 having inputs coupled to the output of the precharge voltage circuits 404 and an output coupled to the output voltage node 604 of the switching regulator 502 and the supply lines of the power amplifiers 510. The power multiplexers are configured to selectively couple the precharge voltage circuit 404 to the supply lines and the output voltage node 604. An exemplary benefit of implementing the power multiplexers 602 is that isolation between the power amplifiers 510 and the precharge voltage circuits 404 may be further improved compared to implementing switches 514 alone to selectively couple the precharge voltage circuits 404.

Referring now to FIG. 7, is a block diagram of an APT voltage regulator circuit 700 using switching regulator output switches, in accordance with certain aspects of the present disclosure. The APT voltage regulator circuit 700 comprises a plurality of output switches 702 having a first terminal coupled to the switching regulator 502 at an output voltage node 704. The plurality of output switches 702 further comprise a second terminal coupled to a respective precharge voltage circuit 404. Each of the precharge voltage circuits 404 are further coupled to the inputs of a plurality of power multiplexers 602. The plurality of power multiplexers 602 are configured to selectively couple a precharge voltage circuit 404 to a respective supply line of each of a plurality of power amplifiers 510. The plurality of output switches 702 are configured couple the output voltage node 704 to the precharge voltage circuit 404 coupled to the supply lines of the power amplifiers 510. An exemplary benefit of the topology of the APT voltage regulator circuit 700 is that power losses associated with the precharge voltage circuits 404 may be reduced by removing switches within the precharge voltage circuits 404, such as the switches 514 in FIG. 5.

Referring now to FIG. 8 is a block diagram of an APT voltage regulator circuit 800 using two adjustable precharge voltage circuits, in accordance with certain aspects of the present disclosure. In one implementation, the precharge voltage circuits 404 each include a precharge voltage regulator 511 configured as an adjustable voltage output push-pull regulator. The push-pull regulator may be configured according to various push-pull topologies such as a push-pull converter, push-pull linear regulator, etc. In operation, the precharge voltage circuits 404 are configured to be alternatively coupled to the output voltage node 503 of the switching regulator 502 to change from a current target output voltage level to the next target output voltage level. For example, precharge voltage circuit 404 a may be coupled to the output voltage node 503 with a stored voltage level corresponding to the current output voltage of the switching regulator 502 while precharge voltage circuit 404 b is decoupled. While precharge voltage circuit 404 b is decoupled, capacitor 512 b is charged to an amount of voltage corresponding to the next output voltage of the switching regulator 502 using precharge voltage regulator 511 b by charging/discharging the capacitor 512 b via the push-pull regulator to the next output voltage. When the output voltage of the switching regulator 502 changes from the current output voltage to the next output voltage, precharge voltage circuit 404 a is decoupled from the output voltage node 503 and precharge voltage circuit 404 b is coupled to the output voltage node 503. After the next following output voltage level is determined, the process repeats by precharge voltage circuit 404 a charging capacitor 512 a to a voltage level corresponding to the next following output voltage level. An exemplary benefit of using two adjustable voltage regulators to switch between a current output voltage and the next output voltage is that the number of precharge voltage circuits needed may be reduced to cover the output voltage range of the switching regulator 502 which may reduce costs and/or area requirements.

Referring now to FIG. 9 is a block diagram of an APT voltage regulator circuit 900 using two switching regulators, in accordance with certain aspect of the present disclosure. The switching regulators 502 a-b may be configured according to the same switching regulator topology. For example, the switching regulators may comprise buck converters using output inductors 504 a-b and output capacitors 506 a-b configured with the same corresponding values of inductance and capacitance. Each of the outputs of the switching regulators 502 a-b are coupled to a first terminal of a respective switch 902 a-b. A second terminal of the switches 902 a-b are coupled to the output voltage node 903. The output voltage node 903 is further coupled to the supply rail of the power amplifier array 508. The APT voltage regulator circuit 900 may further include a capacitor 904 having a first terminal coupled to the output voltage node 503 and a second terminal coupled to ground. In operation, one of the switching regulators 502 is configured to supply a current output voltage while coupled to the output voltage node 903 via a respective switch 902 while the other switching regulator 502 is decoupled from the output voltage node 903 and charging the respective output capacitor 506 to the next output voltage to be provided to the power amplifier array 508. When the next output voltage is needed by the power amplifier array 508, the switching regulator 502 providing the current output voltage is decoupled from the output voltage node 903 while the switching regulator 502 with the output capacitor 506 charged to the next output voltage level is coupled to the output voltage node 903. However, prior to coupling/decoupling of the switching regulators, currents in the output inductors 504 may need to be adjusted to avoid large changes of current at the output voltage node 903. The process repeats where the now decoupled switching regulator 502 will charge the respective output capacitor 506 to the following next output voltage to be provided to the power amplifier array 508.

The capacitance of the output capacitors 506 a-b may comprise a majority of the bulk capacitance of the APT voltage regulator circuit 900 when coupled to the output voltage node 903 whereas capacitor 904 may comprise a substantially smaller capacitance (e.g., 10× smaller). By making the capacitor 904 smaller than the capacitance of output capacitors 506, a voltage error associated with the output voltage may be reduced when switching between the switching regulators 502 a-b as capacitor 904 will constitute a smaller amount of the shared charged with the coupled output capacitor 506.

Referring now to FIG. 10 is a block diagram of an APT voltage regulator circuit 1000 using two switching regulators and a capacitor switch network, in accordance with certain aspects of the present disclosure. The APT voltage regulator circuit 900 comprises a first switching regulator 502 a coupled to an output voltage node 1003, the output voltage node being further coupled to a supply line of a power amplifier array 508 and to an output of a capacitor switch network 1004. A second switching regulator 502 b is coupled to the input of the capacitor switch network 1004. In one implementation, the first switching regulator 502 a is configured source current to the power amplifier array 508 (i.e., the load) while the second switching regulator 502 b is configured to selectively charge capacitors 1006 (i.e., precharge capacitors) of the capacitor switch network 1004. Accordingly, as the second switching regulator 502 b is responsible for charging the capacitors 1006, the second switching regulator may have a reduced sized compared to the first switching regulator 502 a which is responsible for sourcing the current to the power amplifier array 508.

In operation, the capacitor switch network 1004 is configured to selectively couple a capacitor charged substantially to a current output voltage being provided by the first switching regulator 502 a to the output voltage node 1003. The capacitor switch network 1004 is further configured to couple a remaining capacitor 1006 to the output of the second switching regulator 502 b. The second switching regulator 506 b is configured to charge the capacitor 1006 coupled to the output of the second switching regulator 506 b to a next output voltage to be provided by the first switching regulator 502 a. When the first switching regulator provides the next output voltage to the output voltage node 1003, the capacitor switch network 1004 is configured to decouple the capacitor 1006 storing the current output voltage from the output voltage node 503 and decouple the capacitor 1006 storing the next output voltage from the output of the second switching regulator 502 a. The capacitor switch network 1004 will further couple the capacitor 1006 storing the next output voltage to output voltage node 1003 and couple the capacitor 1006 storing the current output voltage to the output of the second switching regulator 502 b. After the next following output voltage to be provided by the first switching regulator 502 a is determined, the second switching regulator 502 b will proceed to charge the coupled capacitor 1006 to the next following output voltage. Switch S1 is configured to selectively couple/decouple capacitor 1006 a from the output of the second switching regulator 502 b while switch S3 is configured to selectively couple/decouple capacitor 1006 a from the output voltage node 1003. Similarly, switch S2 is configured to selectively couple/decouple capacitor 1006 b from the output of the second switching regulator 502 b while switch S4 is configured to selectively couple/decouple capacitor 1006 b from the output voltage node 1003.

It should be noted that while capacitor switch network 1004 of FIG. 10 illustrates two capacitors 1006, any number of capacitors may be implemented in the capacitor switch network.

Referring now to FIG. 11, an example operation of a voltage regulation method 1100 using precharge voltage rails is illustrated, in accordance with certain aspects of the present disclosure. The operations may be performed by a circuit, such as in FIGS. 5-10.

At block 1102, a target output voltage level to be supplied by a voltage regulator is determined. In one implementation, the target output voltage level is based on a signal to be transmitted using one or more power amplifiers. The one or more power amplifiers may be biased using the target output voltage according to an average power tracking (APT) scheme. The APT tracking scheme may be executed on a TX data processor or on a separate processing circuit. The APT tracking scheme determines the target output voltage based on the output power level for a signal to be transmitted. The power level of the signal may vary on a slot by slot basis (e.g., time slot) for transmitting the signal. For example, the APT tracking scheme may determine that the one or more power amplifiers should be biased with a target output voltage of 1.4V for a particular slot of a signal to be transmitted.

At block 1104, the target output voltage is provided via the voltage regulator by at least coupling a precharge voltage circuit having a capacitance charged to a voltage level substantially equal to the target output voltage to a voltage output of the voltage regulator. The charged voltage level may be substantially equal within an error tolerance (e.g., 1% of the target output voltage) and/or include a voltage offset added or subtracted from the target output voltage level. The precharge voltage circuit may be coupled to the voltage output via one or more switches and/or one or more power multiplexers.

At block 1106, a next target output voltage to be supplied by the voltage regulator is determined. For example, the APT tracking scheme may determine that a subsequent slot of the signal to be transmitted may require a different target output voltage to be supplied to the one or more power amplifiers based on the output power level required for the subsequent slot.

At block 1108, the next target output voltage is provided via the voltage regulator by at least coupling a precharge voltage circuit having a capacitance charged to a voltage level substantially equal to the next target output voltage to the voltage output of the voltage regulator. The capacitance may be charged using a fixed or adjustable voltage regulator. The precharge voltage circuit may be coupled subsequent to decoupling the precharge voltage circuit coupled in block 1104.

The various operations of methods described above may be performed by any suitable means capable of performing the corresponding functions. The means may include various hardware component(s) and/or module(s), including, but not limited to one or more circuits. Generally, where there are operations illustrated in figures, those operations may have corresponding counterpart means-plus-function components with similar numbering. For example, means for providing a regulated voltage may comprise, for example, a voltage regulator, such as the switching regulator 502 of FIG. 5. Means for precharging a plurality of voltage rails to a plurality of respective voltages may comprise, for example, a precharge voltage circuit such as the precharge voltage circuit 404 of FIG. 4. Means for selectively coupling a voltage rail of a plurality of voltage rails to the voltage output may comprise, for example, a switch such as switch 514 of FIG. 5 or switch 702 of FIG. 7.

As used herein, the term “determining” encompasses a wide variety of actions. For example, “determining” may include calculating, computing, processing, deriving, investigating, looking up (e.g., looking up in a table, a database, or another data structure), ascertaining, and the like. Also, “determining” may include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory), and the like. Also, “determining” may include resolving, selecting, choosing, establishing, and the like.

As used herein, a phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c, as well as any combination with multiples of the same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b, b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c).

The various illustrative logical blocks, modules, and circuits described in connection with the present disclosure may be implemented or performed with discrete hardware components designed to perform the functions described herein.

The methods disclosed herein comprise one or more steps or actions for achieving the described method. The method steps and/or actions may be interchanged with one another without departing from the scope of the claims. In other words, unless a specific order of steps or actions is specified, the order and/or use of specific steps and/or actions may be modified without departing from the scope of the claims.

It is to be understood that the claims are not limited to the precise configuration and components illustrated above. Various modifications, changes and variations may be made in the arrangement, operation and details of the methods and apparatus described above without departing from the scope of the claims. 

What is claimed is:
 1. A voltage regulator circuit comprising: a first voltage regulator comprising a switching regulator, the first voltage regulator having an adjustable voltage output; an output capacitor coupled to the voltage output; a plurality of precharge voltage circuits each having an output configured to selectively couple to the voltage output, each of the plurality of precharge voltage circuits comprising: a precharge voltage regulator comprising a linear regulator; and a capacitor having a first terminal coupled to an output of the precharge voltage regulator and the output of the respective precharge voltage circuit and a second terminal coupled to a reference potential; and one or more multiplexers, each of the one or more multiplexers having inputs coupled to the outputs of the plurality of precharge voltage circuits and an output coupled to a supply line of one or more power amplifiers; wherein each of the precharge voltage regulators are configured to charge a respective capacitor between different adjustable voltage levels prior to the output of the respective precharge voltage circuit being selectively coupled to the voltage output.
 2. The voltage regulator circuit of claim 1, wherein the first voltage regulator is configured to adjust a voltage level at the voltage output to a next voltage level; and wherein the voltage regulator circuit further comprises logic configured to couple the precharge voltage circuit having a corresponding voltage level to the next voltage level to the voltage output.
 3. The voltage regulator circuit of claim 1, wherein each of the plurality of precharge voltage circuits is selectively coupled to the voltage output by a switch coupled between the capacitor of the precharge voltage circuit and the voltage output.
 4. The voltage regulator circuit of claim 1, wherein each of the plurality of precharge voltage circuits is selectively coupled to the voltage output by a multiplexer coupled to outputs of the plurality of precharge voltage circuits.
 5. The voltage regulator circuit of claim 1, wherein the linear regulator of each of the plurality of precharge voltage circuits comprises a low dropout (LDO) regulator.
 6. The voltage regulator circuit of claim 1, wherein the capacitor of the plurality of precharge voltage circuits comprise one or more precharge capacitors configured to be selectively coupled to an output of the switching regulator.
 7. The voltage regulator circuit of claim 1, further comprising a voltage hub comprising at least two of the precharge voltage circuits.
 8. The voltage regulator circuit of claim 7, further comprising a second voltage regulator having a voltage output; wherein the voltage hub is configured to: selectively couple one of the at least two precharge voltage circuits to the voltage output of the first voltage regulator; and selectively couple another of the at least two precharge voltage circuits to the voltage output of the second voltage regulator.
 9. The voltage regulator circuit of claim 1, wherein the voltage output is coupled to the supply line of the one or more power amplifiers.
 10. A method for regulating voltage using one or more precharge voltage circuits, the method comprising: determining a target output voltage to be supplied by a switching regulator to a power amplifier; providing the target output voltage via the switching regulator by at least supplying a voltage by the switching regulator to a voltage output of the switching regulator having an output capacitor; selectively coupling a first precharge voltage circuit having a capacitor charged to a voltage level equal to the target output voltage of the switching regulator to the voltage output of the switching regulator; selectively coupling the voltage output of the switching regulator to a supply line of one or more power amplifiers via one or more multiplexers; and adjusting the voltage level of the capacitor of the first precharge voltage circuit to a different voltage level using the precharge voltage circuit; wherein the capacitor is charged to the voltage level prior to the first precharge voltage circuit being coupled to the voltage output of the switching regulator.
 11. The method of claim 10, further comprising: determining a next target output voltage to be supplied by the switching regulator; and when the next target output voltage is different than the target output voltage, providing the next target output voltage via the switching regulator by at least: decoupling the coupled first precharge voltage circuit; and coupling a second precharge voltage circuit having a capacitor charged to a voltage level equal to the next target output voltage to the voltage output of the switching regulator after the decoupling.
 12. The method of claim 10, further comprising: determining a next target output voltage to be supplied by the switching regulator; adjusting a voltage level of a capacitor of a second precharge voltage circuit decoupled from the voltage output of the switching regulator to a voltage level equal to the next target output voltage; and providing the next target output voltage via the switching regulator by at least: decoupling the coupled first precharge voltage circuit; and coupling the adjusted second precharge voltage circuit to the voltage output to provide the next target output voltage via the switching regulator.
 13. The method of claim 12, further comprising: determining a voltage offset based on the target output voltage and the next target output voltage; and adjusting the voltage level of the capacitor of the second precharge circuit based on the determined voltage offset.
 14. The method of claim 10, further comprising charging the capacitor of the first precharge voltage circuit to the voltage level by at least: decoupling the first precharge voltage circuit from the voltage output; and supplying a voltage via a voltage regulator of the first precharge voltage circuit to the capacitor.
 15. The method of claim 10, further comprising charging the capacitor of the first precharge voltage circuit to the voltage level by at least: coupling the first precharge voltage circuit to the voltage output; and supplying a voltage via the switching regulator to the capacitor.
 16. The method of claim 15, further comprising maintaining the voltage level of the capacitor by supplying a voltage via a voltage regulator of the first precharge voltage circuit.
 17. A voltage regulation circuit comprising: a switching voltage regulator having a voltage output coupled to a supply line of one or more power amplifiers, wherein the switching voltage regulator is configured to output a target voltage at the voltage output; a plurality of voltage rail prechargers each comprising a capacitor coupled between the voltage output and a precharge voltage regulator, each voltage rail precharger configured to selectively provide a voltage to the voltage output based on a voltage level of the target voltage of the switching voltage regulator; a plurality of switches coupled to the voltage output and one or more multiplexers, each of the one or more multiplexers having inputs coupled to the plurality of switches and an output coupled to the supply line of a respective power amplifier of the one or more power amplifiers; wherein each of the capacitors are charged to a respective voltage prior to being provided to the voltage output of the switching regulator; and wherein the precharge voltage regulator of each of the plurality of the voltage rail prechargers is configured to adjust the charge of the capacitor to the respective voltage level between different voltage levels.
 18. The voltage regulation circuit of claim 17 wherein a voltage rail precharger, of the plurality voltage rail prechargers, configured to provide a voltage corresponding to the target voltage is coupled to the voltage output.
 19. The voltage regulation circuit of claim 17, wherein each of the plurality of voltage rail prechargers is configured to provide a different voltage.
 20. The voltage regulation circuit of claim 19, wherein the switching voltage regulator is configured to charge a respective capacitor in each of the plurality of voltage rail prechargers to the corresponding different voltage.
 21. The voltage regulation circuit of claim 20, wherein each of the plurality of the voltage rail prechargers is further configured to retain the voltage charged on the respective capacitor.
 22. A voltage regulator circuit comprising: means for providing a regulated voltage to a voltage output at a first voltage level; means for precharging a plurality a voltage rails to a plurality of respective voltages; means for selectively coupling a voltage rail of the plurality of voltage rails to the voltage output corresponding to the first voltage level of the regulated voltage of the means for providing; and means for adjusting one or more voltages of the plurality of respective voltages to a different voltage; wherein the precharging of the respective voltages occurs while the means for precharging a plurality of voltage rails is uncoupled from the voltage output.
 23. The voltage regulator circuit of claim 22, wherein the means for precharging comprises means for storing the plurality of respective voltages.
 24. The voltage regulator circuit of claim 23, wherein the means for precharging further comprises means for retaining the voltage stored in the means for storing. 